This follow-up sampling was carried out in order to:
1. Confirm the results of the NURE sampling and USGS chemical re-analyses of the NURE samples. On rare occasion on other projects, DIR has found the NURE era sampling work to be marred by sample mis-labelling and/or map location errors. (The NURE sampling work took place before the mapping convenience and relative accuracy of satellite GPS.)
2. Fill in gaps in the NURE stream sediment sample coverage. The Carter administration’s NURE program sampling was intended as reconnaissance-stage work only. Consequently, there are large areas of rock in Nevada (and elsewhere in the US) not represented in the NURE sampling coverage, and it is therefore usually not possible to fully define the extent of mineralization-related geochemical alteration surrounding NURE anomalies using first-pass NURE stream sediment sampling data only.
3. More closely define the rock source of geochemical anomalies discerned in the NURE/USGS data set. Some of the drainage cells sampled in the NURE program are as large as 15 square miles. Without follow-up subsampling, it is not possible to locate the specific rock area generating the mineralization-related geochemical anomaly.
Interestingly, this October follow-up sampling work provided some early encouragement concerning DIR’s exploration innovation. For example, the first project area sampled was, according to Nevada geological map coverage, supposed to be located in a large felsic intrusive body. Instead, as would be expected by the particular nature of the NURE geochemistry for that area, this anomalous drainage was found to be underlain by a strongly carbonaceous silty limestone, a limestone like those very frequently associated with Carlin-type gold deposits.
Also encouraging was the finding that two other NURE anomalies sampled during the month were located in long- to recently-abandoned mineral prospects marked by drill roads and drill pads. The younger of these two unstaked mineral prospects showed recent evidence of detail-scale geophysical and/or geochemical surface surveying (i.e., fresh survey line flagging).
Finally, it turned out that the geochemical data obtained from summer 2015’s sampling of drainage cells containing Carlin-type gold deposits that were missing from the NURE/USGS north central Nevada sample set are incompatible with the original NURE/USGS geochemical analyses. This problem is believed to be the result of basic differences in sample prep, sample digestion, and sample analysis procedure differences existing among the various labs involved. Fortunately, as shown in the two graphs below, each data set is internally consistent and permits statistical estimation of Carlin-type geochemical data production functions permitting close (90% adjusted r-squared) gold resource interpretation of Nevada stream sediment data. The NURE/USGS geochemical data production function for Carlin-type was, as first mentioned, used by DIR to filter the 10,000+ stream sediment samples for likely locations of undiscovered economically-mineralized Carlin-type gold deposits. On the other hand, the Carlin-type gold deposit production function, derived from summer 2015 sampling by DIR and analyses by ACME/BV Labs, will be used to interpret the geochemical data from DIR follow-up and infill stream sediment sampling work.